Mordenite is one of a number of catalysts commonly employed in the transalkylation of alkyl aromatic compounds. Mordenite is a crystalline alumino silicate zeolite having a network of silicon and aluminum atoms interlinked in its crystalline structure through oxygen atoms. For a general description of mordenite catalysts, reference is made to Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Edition, 1981, under the heading “Molecular Sieves”, Vol. 15, pages 638-643. Mordenite, as found in nature or as synthesized, typically has relatively low silica to alumina mole ratio of about 10 or less. Such conventionally structured mordenite catalysts can be employed in the disproportionation of toluene. However, mordenite catalysts having a substantially lower alumina content can also be employed in the disproportionation of toluene.
Hydrogen, along with toluene, may be supplied to the reactor in which the toluene disproportionation reaction is carried out. While the disproportionation of toluene to benzene and xylene has no net change in hydrogen, a hydrogen co-feed or input may be employed in order to prolong the useful life of the catalyst. In addition to the benzene and mixed xylenes content of the feedstock, non-aromatic compounds may also be formed as a side reaction. Even relatively low non-aromatic levels of about 1-2 wt. % can lead to rapid catalyst deactivation and thus should usually be avoided.
Mordenite modified by the inclusion of a metallic component such as nickel can be employed in the disproportionation of toluene containing feedstocks. The disproportionation of toluene feedstocks may be carried out at temperatures ranging from about 200° to about 600° C. or above and at pressures ranging from about atmospheric to about 100 atmospheres or above. Operating conditions may vary depending upon process parameters such as space velocity and hydrogen/toluene mole ratio and the silica/alumina ratio of the mordenite catalyst. Where the silica alumina ratio is relatively high, toluene disproportionation reactions may be carried out at somewhat lower temperatures than when the silica alumina ratio is relatively low.